The invention relates generally to a prosthesis.
More particularly, the invention relates to an internal prosthesis for the total or partial replacement of a bone.
A known type of prosthesis for the partial replacement of a bone consists of a rod-like member which is provided with an abutment member at one end thereof. The rod-like member is embedded in the bone which is to be partially replaced while the abutment member bears against an adjacent bone.
This type of prosthesis is used when one end of a bone is defective and the other end is healthy. The prosthesis is embedded in the bone to a distance which depends upon the physical characteristics of the patient. In this manner, account is taken of the fact that the distance to be bridged by the prosthesis is different for different patients.
A known prosthesis for the replacement of an entire bone, e.g., for the total replacement of a femur, has a rod-like member which is provided with an abutment member at either end. Each of the abutment members bears against one of the bones which is located adjacent to the bone being replaced. The length of the prosthesis must be such that the distance between the bones engaged by the abutment members remains substantially unchanged from before. The reason is that changes in this distance generally cause discomfort to the patient. For instance, an improperly dimensioned replacement for the femur can cause one leg of the patient to be longer than the other.
Occasionally, difficulties arise with the preoperative measurements required to establish the length of the prosthesis. Consequently, errors in measurement cannot always be avoided. In extreme cases, the errors may be so large that the prosthesis cannot be implanted and a new prosthesis must be constructed.
In some cases, a bone has defects at both its proximal and distal ends but not in the middle. While it is desirable to retain the middle part of the bone, this part of the bone is frequently so short that it is not possible to secure a prosthesis thereto. Accordingly, the entire bone must be replaced by a prosthesis.